There are a lot of ways to fix issues with your browser, but they often require you to delete all your data—stored passwords, cookies, form history, and other things that take awhile to build back up. Firefox's Beta and Aurora channels now have a new feature called "Reset Firefox", which lets you start fresh while still keeping some of your old information.

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Firefox Reset essentially starts you off with a new profile, then migrates some of your data back from your old profile. This includes:

Cookies

Browsing History

Saved Form History

Saved Passwords

Bookmarks and Bookmark Backups

These are usually not the kind of data that cause problems, so there's no harm in restoring them. It does not restore your extensions, preference tweaks, or about:config hacks—but it makes it easy to print out a list of them before you reset the browser. Then, you can start adding those back in one by one. As soon as you notice the issue that was plaguing your browser before, you know what the culprit is and can then move on accordingly.

To reset Firefox, just head to about:support and click the "Reset Firefox" button in the top right-hand corner. If you want to save your list of extensions and about:config tweaks, you should click the "Copy to Clipboard" button or print the about:support page first (mine listed most of my tweaks, but not quite all of them). When you reset, it'll let you know what it's going to restore, then quit Firefox. When you open it back up, you'll have a clean slate from which you can start rebuilding.

Right now this feature is only in the Beta and Aurora channels of Firefox, and Mozilla says the Beta channel is the only one that's been tested and known to be stable. It'll make its way to the other channels soon, but for now, you can hit the link below to read more, see Mozilla's support page for detailed information, or hop on over to about:support and try it out for yourself if you've bee putting off a profile reset.